Physiological Entomology最新文献

During mating in the Lepidoptera (moths and butterflies), sperm are passed to the female via a copulation in which the male transfers a large and often complex spermatophore over the major part of an hour or more. Subsequently, over the course of an hour or often considerably more, the sperm exit the spermatophore and travel over a relatively complex route to the spermatheca, where the sperm are stored and then used as the eggs are laid. The process of spermatophore formation and migration of sperm in the female has been described in many Lepidoptera, but the mechanics involved have received less attention. Understanding these is important in discerning the relative roles of males and females in determining the outcome of matings. We describe how the spermatophore is formed, how the sperm migrate in the female, and the fate of the sperm in the spermatheca of the tobacco hornworm moth, Manduca sexta. We found that sperm movement from the spermatophore relied upon motility of the sperm, but further movement of the sperm to the spermatheca was dependent on female muscular action. After arriving in the spermatheca, the anucleate parasperm (apyrene sperm) separated into the lateral pouch of the spermatheca (lagena) and disappeared over 7 days, whereas the eusperm (eupyrene sperm) persisted in the central lumen of the spermatheca (utriculus). The relative persistence of these two sperm types could shed some light on what determines the proclivity of females to remate. Elucidation of these physiological mechanisms contributes to an understanding of the mechanisms of female choice and male competition in Lepidoptera.

Reduced temperatures increase longevity in cold-tolerant insects, but insects that are not cold-tolerant experience elevated mortality at constant low temperatures. Fluctuating thermal regimes (FTRs) increase longevity in many insect species while slowing or delaying development and senescence. Under FTR insects are held at low temperature with a daily warm pulse of increased temperature. The model organism Drosophila melanogaster is widely used for diverse research activities and numerous transgenic strains have been developed and must be maintained in continuous culture at stock centres. We measured the effect of FTR that oscillates between 6 and 22 °C on the longevity and fertility of adult D. melanogaster versus a constant temperature of 6 and 22 °C. We demonstrate that FTR increases mean longevity by 8.8-fold compared to a constant 6 °C and by 5.9-fold to a constant 22 °C. We assessed male and female fertility of FTR treated adults from 20 to 100 days at 20 day intervals and constant temperature treated adults after 7 days. Under FTR males exhibited increased fertility peaking at 80 days before dropping significantly at 100 days. Mean female fertility declined steadily under FTR but remained at 53% of constant temperature-treated flies after 60 days. The increased male fertility remains unexplained. Fertility of the offspring of FTR-treated adults did not differ from flies reared at constant 22 °C. FTR extends generations and cultures incubated under this protocol can establish new cultures. FTR can be used to further investigate the accumulation and mitigation of chill injury and is suitable for reducing maintenance in stock centres.

The tomato leaf miner, Tuta absoluta (Meyrick), is one of the serious insect pests in tomato and potato farms. Along with acute toxicity, effects of emamectin benzoate alone and mixed with some conventional insecticides on esterase enzymes and the protein content of T. absoluta second-instar larvae were assessed in the current study. After 72 h exposure time, emamectin benzoate had the most toxicity (LC₅₀ = 0.52 mg a.i. L⁻¹), followed by azadirachtin (LC₅₀ = 5.19 mg a.i. L⁻¹), indoxacarb (LC₅₀ = 7.13 mg a.i. L⁻¹), imidocloprid (LC₅₀ = 44.63 mg a.i. L⁻¹), thiacloprid (LC₅₀ = 293.92 mg a.i. L⁻¹) and lambda-cyhalothrin (LC₅₀ = 610.08 mg a.i. L⁻¹). Although emamectin benzoate mixed with either azadirachtin or indoxacarb at LC₁₅: LC₁₅ (Lethal Concentration to kill 15% tested insects) ratio had synergistic effects, its combination with imidacloprid or thiacloprid showed additive interactions. However, emamectin benzoate mixed with imidacloprid at both LC₂₅: LC₂₅ and LC₅₀: LC₅₀ ratios showed synergistic effects. Lambda-cyhalothrin mixed with emamectin benzoate showed an antagonistic interaction in all tested ratios. α-esterase activity of larvae increased when emamectin benzoate was mixed with thiacloprid in comparison with emamectin benzoate alone and the control. Combinations of emamectin benzoate with either azadirachtin or indoxacarb significantly reduced the total protein content of larvae. Generally, it can be concluded that the combination of emamectin benzoate with either azadirachtin, indoxacarb, or imidacloprid resulted in more negative impacts against T. absoluta larvae.

In Lepidoptera, it is known that larval and pupal testes enlarge in volume and then decrease in size over various phases of the pupal stage. After adult emergence, testis shrinkage continues. In the present study, the effects of temperature, age and stage on testis development were investigated in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae). Laboratory experiments indicated that in the adult stage, testis shrank markedly with age and with increasing temperatures, when males were reared at 15, 20, 25 or 30 °C during the larval and pupal stages and then transferred to other temperatures. When kept at 15, 20, 25 or 30 °C throughout their entire life (larva, pupa and adult), the higher the temperature, the smaller the testis volume at any given adult age, indicating that larval and/or pupal rearing temperatures also affected testis development. Field experiments carried out in Tokyo showed that testis volume in wild adult males of diamondback moth was quite varied, suggesting that this population had both young and old males at each survey time. The lower the larval and pupal rearing temperature, the larger the adult, as measured by forewing length. Since larger adults tended to have larger testis at adult emergence, adult testis volume should be compensated based on the forewing length. Mating reduced the testis size. Our results suggest that adult age of diamondback moths in wild populations can be estimated roughly from the data on testis volume, temperature and forewing length.

Temperature is among the most influential factors in animal biology, and especially thermal fluctuations are key determinants of life history traits for ectothermic organisms. Diet characteristics add complexity to the effect of temperature on animals' life history traits. This is even more intricate in phytophagous insects that develop inside hosts. Here, using the seed beetle Zabrotes subfasciatus Boheman we tested life history trait response to five different ambient temperatures (15, 25, 30, 35, and 45 °C). We also tested the effect of the interaction between temperature and diet on the weevils' life history traits and estimated fitness for individuals at different temperature and food supplementation conditions. We first showed that the relationship between temperature and egg size and number, and adult emergence is altered by sugar ingestion, mainly at 30 °C. Additionally, we showed that temperature and sugar ingestion have opposite effects on longevity, with this trait being heightened by sugar ingestion at 25 °C. Interestingly, except at 35 °C, egg size shows a response that opposes the temperature-size rule, which states increasing environmental temperature reduces insect's size. Finally, excluding the extreme temperatures, fitness patterns increased with temperature and the clearer effect of parental feeding on fitness was registered at 30 °C. Since 30 °C is the temperature at which our weevil populations are maintained in the laboratory, these results point to a possible long-term “acclimation effect” on the weevils' fitness. Thus, testing the effect of the temperature experienced by the original population on the experimental weevils' fitness might shed light on the biological explanation of the observed temperature vs diet interaction.

Carbohydrate plays an important role in rice resistance or tolerance to pests, and also affects the continuous feeding of brown planthoppers (BPHs) on rice. However, the change in the sugar metabolism of BPH and rice plant after BPH infestation is not well studied. In this study, the rice variety Taichung Native 1 (TN1) was taken as a control group, and four kinds of common rice varieties in Zhejiang province (China), Zhong Jiazao 17 (ZJZ17), Zhong Zheyou 8 (ZZY8), Tian Youhuazhan (TYHZ), and Jing Liangyouhuazhan (JLYHZ), were taken as experimental group. The results showed that the BPHs best preferred the TN1 rice variety. BPHs in fifth instar feeding on the other four rice varieties had lower levels of trehalose, glucose, and glycogen, and the difference in sugar levels further resulted in differences in trehalose-6-phosphate synthase and trehalase expression and trehalase activity. In addition, after BPHs infestation, the glucose content in the sheath at 30 days decreased, while it increased in the sheath at 60 days. Moreover, the trehalose content in the sheath at 30 and 60 days decreased. The starch in the leaves at 60 days also decreased. This study demonstrated that both BPHs and rice plant showed changes in carbohydrate metabolism after BPHs feeding on rice, but these changes varied with rice varieties and rice growth stage. These results provide a basis for a better understanding the physiological interaction between BPH and rice plant.

The larger grain borer, Prostephanus truncatus (Horn) is an invasive insect pest species of global economic concern. It however remains unknown how P. truncatus succeeds under increasing temperatures and desiccation effects associated with projected climate change. Here, we investigated the effects of desiccation and high-temperature stress on physiological fitness of P. truncatus larvae and adults. Specifically, we measured critical thermal maxima, heat knockdown time and water loss rates following heat and desiccation acclimation. Results showed beneficial heat acclimation effects on heat tolerance (critical thermal maxima and heat knockdown time). Similarly, desiccation acclimation significantly improved both heat tolerance traits, indicating cross-tolerance effects, not for heat knockdown time in larvae. In all cases, adults exhibited more improved heat tolerance than larvae. Conversely, heat acclimation increased water loss rates, and more so in larvae than adults. Improved heat tolerance plus abiotic stress cross-tolerance of P. truncatus may explain its enhanced physiological and ecological fitness in dry tropical and changing climate environments. These results are important in explaining the role of physiology in insect invasions and may inform pest management and forecasting.

The role of Pseudomonas aeruginosa alkaline protease, one of the important virulence factors of these bacteria, in the prophenoloxidase (proPO) system activation in Galleria mellonella haemolymph was investigated. Immunization of G. mellonella larvae with alkaline protease led to an increase in phenoloxidase (PO) activity in haemolymph 2–8 h after the injection. However, 15 h after the challenge, almost no PO activity was detected, in contrast to insects immunized with heat-killed P. aeruginosa, where an elevated PO activity in haemolymph persisted at all the time points of the experiment (2–24 h). To test the effect of alkaline protease on already activated PO in vitro, non-immune G. mellonella haemolymph with proPO system pre-activated in vitro by heat-killed P. aeruginosa was used. Subsequently, direct incubation of the protease with non-immune haemolymph was carried out to test the effect of the alkaline protease on the proPO system activation. It can be postulated that P. aeruginosa alkaline protease affected not only the active PO, but also significantly inhibited proPO cascade activation in the haemolymph of G. mellonella.

The damage of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), causes is mainly determined by the success of its overwintering. The aim of our study was to assess the consequences of the artificial cooling on the movement and survival ability of overwintering larvae of O. nubilalis by using computer-assisted tomography. The in situ movement of the examined larvae in icy media of different thickness (5, 15, and 30 cm) and during freezing periods of 5, 10, 20, 40, and 60 min was determined in maize stalks using CT and the positioner-laser of the CT apparatus. It has been found that the thickness of the ice had a significant effect on the displacement of the overwintering larvae, however, the impact of the duration of freezing on the moving of the larvae could not be proven statistically. Enhanced larvae activity due to thinner ice layers (5, 15 cm) were of exponential type, which was more pronounced just prior to the freezing point. In contrast, thicker ice covering (30 cm) caused complete immobility. According to our results, the diapausing larvae were still able to move and albeit it appeared to be capable of surviving the direct impact of extreme cold, it could even leave its overwintering place as a result of low temperature. Furthermore, the maize stalk tissue contributes to the survival-success of the larvae as it seems to act as a temperature-buffer moderating the severe impact that low temperature exerts on living tissue.